Workpiece stocker with circular configuration

ABSTRACT

An improved stocker configuration for storing workpieces in a fabrication facility is disclosed, employing workpiece compartments arranged stationarily around a robot handling assembly. The robot handler can be designed with three degrees of freedom, to improve speed, throughput and minimum particle generation. In addition, the stocker storage area is stationary with the movable components are the robot assembly, thus further contributing to the cleanliness of the storage stocker. The stocker configuration can be open storage area for fast access, space saving and ease of clean air purging. The stocker configuration can provide highly dense workpiece storage, utilizing a circumferential edge gripper robot handling assembly.

This application is a continuation of application Ser. No. 11/811,372,filed on Jun. 9, 2007, which claims priority from U.S. provisionalpatent application Ser. No. 60/859,202, filed on Nov. 15, 2006, entitled“Workpiece stocker with circular configuration”; and from Germany patentapplication 10 2006 028 057.1, filed on Jun. 9, 2006, entitled“Vorrichtung zum Lagern von kontaminationsempfindlichen, plattenformigenGegenstanden, insbesondere zum Lagern von Halbleiterwafern”; which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to apparatuses and methods to store andtransfer objects, and more particularly to workpiece stockerconfigurations such as stocker for semiconductor wafers, reticles orcarrier boxes.

BACKGROUND

Stockers generally are installed within a semiconductor facility fortemporarily storing workpieces, such as wafers, flat panel displays,LCD, photolithography reticles, or masks. In the process ofmanufacturing semiconductor devices, LCD panels, and others, there arehundreds of processing equipments and thus hundreds of manufacturingsteps. It is very difficult for the flow of the wafers, flat panels, orLCDs (hereafter workpiece) to be uniform from step to step, from tool totool. Despite the best planners, there is always the unexpectedscenario, such as a tool down, an emergency lot coming through, aperiodic maintenance lasting longer than planned, thus there are variousaccumulations of the workpieces at certain steps for certain tools. Theaccumulated workpieces will need to be stored in a storage stocker,waiting to be processed.

Further, photolithography process is a critical process in thesemiconductor fabrication facility, involving a large number ofphotolithography masks or reticles (hereinafter reticle). The reticlesthus are typically stored in a storage stocker, and being retrieved whenneeded into the lithograpahy exposure equipment.

The storage of workpieces and reticles (hereafter articles) is much morecomplicated due to the requirement of cleanliness. Damages to thearticles can be physical damages in the form of particles, or chemicaldamages, in the form of interactions. With the critical dimension of thesemiconductor device processing surpassing 0.1 micron, particles of 0.1micron sizes, and reactive species will need to be prevented fromapproaching the articles. The storage areas typically would need to beeven cleaner than the processing facility, to ensure less cleaningbetween processing.

Thus the stocker storage areas is typically designed to be sealed offfrom the outside environment, preferably with constant purging, and evenwith inert gas flow to prevent possible chemical reactions. Access tothe storage areas is load-locked, to ensure isolation between the cleanstorage environment and the outside environment.

SUMMARY

The present invention discloses an improved stocker configuration forstoring workpieces in a fabrication facility, especially a wafer stockeror a reticle stocker for semiconductor processing. In an exemplaryembodiment, the workpieces are stored stationary around a robot handlingassembly, preferably substantially circular. In this configuration, therobot handler can be designed with three degrees of freedom, e.g.radial, rotational and vertical movements, thus can have improved speedand throughput. Three degree of freedom robots are well established withminimum particle generation, thus this configuration can providecleanliness for workpiece storage. In addition, the stocker storage areais stationary with the movable components are the robot assembly, thusfurther contributing to the cleanliness of the storage stocker.

In an embodiment, the stocker configuration provides an open storagearea with the workpieces stored bare for easy access. The storing ofbare workpieces provides fast access, space saving and ease of clean airpurging. The storage area can be configured with a plurality of opencompartments, arranging surrounding a robot handling assembly, also inthe vertical direction.

In an embodiment, the stocker configuration provides the storage of theworkpieces in a highly dense configuration, in either vertical orhorizontal positions. The stocker provides a circumferential edgegripper robot handling assembly, approaching and picking up theworkpieces from the circumferential edges, thus allowing the denseworkpiece storage configuration.

The storage area can include clean air delivery system flowing inwardtoward the center, such as the robot handling system. This inward flowconfiguration reduces particle contamination since there is no particlegeneration upstream of the clean air flow. Further, the storage area canbe partitioned into a plurality of sections based on cleanliness, forexample, a top section for ultra clean storage, a middle section fornormal clean storage, and a bottom section for dirty storage. The flowconfiguration can be designed for minimizing cross contamination betweenthese sections.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of the stocker according to thepresent invention.

FIG. 2 shows an exemplary stocker with opened door for the manualwithdrawal of a container.

FIG. 3 shows a cross section of a container for a stocker (line III-IIIin FIG. 4).

FIG. 4 shows another view of a container.

FIG. 5 shows a top view of a robot handling assembly unit.

FIG. 6 shows a side view of a robot handling unit.

FIG. 7 shows another embodiment of the stocker according to the presentinvention, top view.

FIG. 8 shows another embodiment of the stocker according to the presentinvention, top view.

FIG. 9 shows a side view of an exemplary stocker with two robotpositions.

FIG. 10 shows a side view of an exemplary stocker with clean gas flowconfiguration.

FIG. 11 shows a top view of another exemplary stocker.

FIG. 12 shows a side view of another exemplary stocker.

FIG. 13 shows a top view of another exemplary stocker.

FIG. 14 shows a side view of another exemplary stocker.

DETAIL DESCRIPTIONS

The stocker according to an exemplary embodiment of the presentinvention is designed for storing contamination-sensitive wafer shapearticles such as semiconductor wafers, and reticles. The stockerdesigned is particularly configured for space-saving storage andflexible handling. The stocker, in particular, is well suitable forstoring a large number of 300 mm or larger wafer on a small storagespace under clean conditions.

In an embodiment, the stocker provides that the articles, such assemiconductor wafers, can be stored openly in the clean storage area,together with the robot handling assembly. The robot handling unit thuscan access very fast the individual articles and to pick up and placethem in carrier boxes. The open storage concept can provide high densitywith small footprint storage.

The open storage can be partitioned into compartments to reduce the riskof cross contamination. The compartments can include storage containers,fastened to carrier racks. The stationary of the carrier racks, thestorage containers, the compartments and the articles prevent particlesgenerated from motions, thus substantially reducing the risk ofparticles generated by abrasion, movement and cross contamination airflow.

The storage containers are preferably shaped as a open, box-likecontainer, where the robot handling unit can be adapted optimally toinserting and taking articles out of the storage containers. In apreferred embodiment, the containers are designed for highly densestorage of articles, for example semiconductor wafer with a pitchdistance of less than 5 mm, preferably about 2.5 mm or less. The storagecontainers are arranged in a shelving configuration surrounding therobot handling unit, and preferably approximately circular. The storagecontainers can be arranged in a x-y array, with the shelves openingsfacing a robotic mechanism for transferring the articles. The stationarystocker comprises a plurality of vertically and horizontally spacedshelves each for storing a plurality of articles. The shelves can alsodesigned for storing a plurality of containers where the articles arestored within.

This configuration can provide space-saving arrangement and at the sametime high storage capacity. In addition a very fast accessing of storedarticles can be possible in this configuration. The particularlypreferred configuration of circular arrangement of the storagecontainers is well suited with a three degree of freedom robot such as aSCARA robot. The robots includes articulated arms, mobile in ahorizontal plane with rotational and radially to a center point. Therobot can also be a six axis robot.

Robot assemblies are an important component in automation, especially inmanufacturing facilities and manufacturing equipments. For example, inthe semiconductor industry, robot arms are used to handle semiconductorwafers, flat panel display, LCD, reticles, masks, or carrier boxes.

In the semiconductor fabrication facility, robot can be used totransport workpieces, typically stored in carrier boxes, from onelocation to another location, from one equipment to another equipment.In a process system, a robot is typically used to remove the workpiecesfrom the carrier boxes, and then loaded into a loadlock. Another robotcan be used to move the workpiece from the loadlock into a processingchamber, and from one processing chamber to another processing chamber.Thus within a processing system, there might be a plurality of robots,each one is designed for a particular task. The processing system couldbe a deposition system, an etch system, a lithography system, ametrology system, an inspection system, an implantation system, atreatment system, or any workpiece processing system.

Generally speaking, robot handling assembly are different for vacuumsystem and atmospheric system. The stocker, designed for storing theworkpieces until needed, is typically an atmospheric system where arobot is typically used to remove the workpieces from the carrier boxes,and then loaded into a loadlock. Another robot can be used to move theworkpiece from the loadlock into a storage chamber, where the workpiecesare stored without the original carrier boxes. For box stocker system,the workpieces are stored together with the carrier boxes, without theneed for removing them out of the carrier boxes.

The robot mechanism can comprises articulate arm joints to move anarticle or a container into and out of the stationary stocker. Further,the robot arm assembly comprises a flexible multiple-link mechanism,designed to reach the shelves of the stocker. The arm assembly can haveindependent radial and rotational movements to reach the arranged spacesof the stocker.

The stocker of the present invention provides storage containers formingapproximately a substantially circular cabinet around a robot handlingdevice. The robot assembly is preferably stationary, with articulate armjoints reaching the inner side of the stationary stocker to transferarticles.

The surrounding, e.g. circular, arrangement of the stocker allows theuse of vacuum robot, thus the robot assembly is less likely to generateparticles within the stocker storage area. The stocker further comprisesloadlock station to isolate the outside environment. This configurationafforts the articles stored in the radial path of a robot, thusproviding fast picking up and placing articles. Plus, the control of therobot handling assembly is greatly simplied and programmed.

The stored articles can also be arranged in a circular configuration,thus providing a smaller pitch in the inner surface than the outerpitch. The articles then are position in V-shaped in the storagecontainer relative to each other, thus can be effectively cleaned with aclean gas flow from the outside to the inside.

The robot handling unit includes vertical movement to access thevertical storage containers. The stocker can also include a secondhandling unit for transferring the articles into or from the containers.The stocker can include backside doors for accessing the back of thearticle containers. The back doors allow access to the articles inemergency events, such as a system crash. The stocker can include ablower for producing a continuous clean gas flow toward the containers,and preferably blowing contamination efficiently downward.

An exemplary stocker 10 is shown in FIGS. 1 and 2. The stocker 10includes a housing 12, containing a robot handling unit 14 and a carrierrack 16 to support a plurality of article containers 18. The housing 12surrounds the robot handling unit 14, the carrier rack 16 and thecontainers 18 to form complete enclosure for a clean environment. Thetop of the housing can be provided with blower and filters (not shown)to produce within the housing 12 a flow of clean air from the top to thebottom.

Each container 18 is designed to store a plurality ofcontamination-sensitive articles. In a preferred embodiment, thearticles are semiconductor wafers, which can be stored vertically in thecontainer 18. In an exemplary embodiment, each container can hold 100wafers of 300 mm. The distance between the stored wafers can be a littleas 2.5 mm.

The robot handling unit 14 can be a radial, rotational and verticalrobot, or can be a 6-axis robot, located in a corner of the housing 12.The carrier rack 16 with the containers 18 are forming a C-shapesurrounding the robot handling unit 14. In FIG. 2, two doors 22 arelocated in the side panels of the housing 12 to provide manual access tothe containers 18 from the rear of the housing. A container 18′ is shownin FIG. 2 to be removed from the carrier rack by the doors 22 comprisingdoor panels 22 a and 22 b. A mobile clean area and an appropriateenclosure (not shown) can be provided before the withdrawal of thecontainer 18′ to prevent exposure to the external contaminants.

The stocker 10 can further comprise a pre-aligner 28 for aligning awafer 20. The wafer 20 can be taken in and out of the pre-aligner 28 bya door 30, connected to a FOUP 32.

FIGS. 3 and 4 show an exemplary embodiment of a container 18, whichincludes a rear wall 38, a bottom wall 40 and two side panels 42, 44.The rear wall 38 and the bottom wall 40 preferably provides an opening46 for releasing clean air flow diagonally across the wafer 20. The airflow 48 between the individual wafers 20 passes through and ensures thatany existing particles and foreign matter are removed diagonallydownward from the container 18.

Within the container 18 four comblike components with splits 50, 52, 54,56 are arranged. The split 50-56 are arranged to hold a wafer by itsdown and back side to permit the removal of the wafer with the robothandling unit 14.

At the upper corner area, there exists a recess 58 to insert a retainer60. The retainer 60 is designed to hold the wafers in place duringmovement of the container 18. Each container 18 may have a handle (notshown), which is connected with the retainer 60, so that a withdrawal ofthe container 18 is only possible if the retainer 60 is inserted in therecess 58.

FIGS. 5 and 6 shows an exemplary robot handling unit according to thepresent invention. The integrated grip arm 14 possesses a first gripperarm 24 and a second gripper arm 26. The first gripper arm 24 is designedas a grip arm, where a wafer 20 a can be seized at the edges in avertical position. The grip arm 24 surrounds the wafer 20 a at its outercircumference in an exemplary C-shaped. Two grip elements 64 and 66 arearranged at the free ends of the grip arm 24. The grip arm 24 surroundsthe wafer 20 a along a circular arc “alpha” of more than 180°. The gripelements 64, 66 can hold the wafer 20 a therefore without firm wedgingand essentially alone due to gravity. For the pick up and placement of awafer 20 a in a carrier box 18, the grip elements 64, 66 can be opened.In this figure, only the grip element 66 is mobile.

The second gripper arm 26 comprises a Y-shape arm with grip elements 68,70 at the ends. The gripper arm 26 is holding a wafer in different plane72 than the gripper arm 24. A wafer 20 b is held by the grip elements68, 70 in the plane 72. The gripper arm 26 has a free end, thus canenter a FOUP to pick up or placing a wafer.

The grippers 24 and 26 are arranged at the free ends of an L-shaped armsegment 74 of an integrated grip arm 14. The arm segment 74 can beswiveling around an axle 76, which lies coaxially to a leg of the armsegment 74, where the gripper 24 is located. This arrangement makes itpossible to take and by a 90° rotation around the axle 76, bringing awafer 20 a into a horizontal position out of a vertical position fromthe carrier box 18. The integrated grip arm can then transfer the waferto a horizontal station, for example, the pre-aligner 28 in FIG. 1 or 94in FIG. 8. The integrated grip arm then switches gripper, and thegripper 26 can pick up the wafer and transfer to a FOUP. Wafers from theFOUP can be brought into the carrier box 18 by reverse operations. Theintegrated grip arm thus can provide movement of the wafers from a FOUPto the storage area with the grippers 24 and 26.

The stocker 10 can provide random access to the stored wafer, thus caneliminate the need for a sorter. In particular, the robot handling unit14 is capable of selecting wafers 20 from arbitrary containers 18 into aFOUP 32. The stocker 10 thus can be integrated with a FOUP front endloader. Due to the vertical storage and the associated high densitystorage arrangement of the wafers, the stocker can achieve high storagecapacity with small footprint. The storage of the individual wafers inopen, separate, box shaped container ensures that cross contaminationbetween different wafers 20 is difficult despite the open storageconfiguration.

FIGS. 7 and 8 show exemplary embodiments of the present inventionstocker 80, comprising a plurality of containers 81 surrounding a robothandling unit 82 in a circle. The handling unit 82 is depicted with aSCARA robot 87 with an articulate arm 84, that can move radially in ahorizontal plane parallel to the view level. The articulate arm 84 isswivelling around an center point 86, which defines a circulararrangement of the containers 81. Thus the articulate arm 84 can providemovements within the horizontal plane, radially and rotationally to thecenter point 86. The articulate arm 84 is arranged pick up and to placearticles 20 in radial direction in and out of containers 81.

FIG. 8 is a plan view on the exemplary stocker 80 along a cutting plane,e.g. the cutting plane VIII-VIII from corresponding FIG. 9. In thisplane, some containers 81 are missing from the circular arrangement. Inthese spaces, a second handling unit 92 and a Prealigner 94 can beprovided.

The robot handling unit 82 is designed to transfer a wafer from acontainer 81 to the Prealigner 94. In addition the robot handling unit82 can rotate the wafer, taking a vertical stored wafer in the container81 to a horizontal stored wafer position on the Prealigner 94. Thesecond handling unit 92 can be used to transfer the wafer from thePrealigner 94 to the FOUP 32. It is preferable that the load lockstation 96 possesses a hermetic connection to the housing 12, so thatthe wafer 20 can be transferred into the FOUP 32 contamination-free.

The second handling unit 92 can also be a robot with an articulate arm,radially movable to a center point to move the wafer between thePrealigner and the FOUPs.

The load lock input/output station 96 can include two FOUP 32. Thisconfiguration can provide the functionality of a sorter, providing themeans to relocate and sort wafers 20 between two FOUPs 32.

The stocker storage system is designed so that the storage area is freeof movement components, circuitry, and other contaminant generatingparts. Further, the air flow is filtered before entering the storagearea, and the storage area is designed to have a laminar air flow on thesurfaces of each workpiece, thus ensuring that there is no upstreamcontamination generation source. The clean air flow is then passing theworkpieces toward the robot handling unit, which is located in thecenter of the storage area, downstream of the clean air flow. Thus themovement of the robot handling unit does not contribute to any particlegeneration within the clean air flow path over the workpieces. Othercomponents associated with the operation of the stocker system arelocated external to the storage unit and downstream of the air flow overthe workpieces.

To further removing particles from the workpieces, air flow accelerationmight be created when the air exits the workpieces. Thus the workpiecescan be arranged to form wedge shape storage area with the entrancelarger than the exit. When the air flow passes through the workpieces,it accelerates through the restricted opening, and thus dislodgingparticles toward the center exhaust area. The vertical arrangedworkpieces 20 as shown in FIGS. 7 and 8 are positioned radially from thecenter, thus they are not parallel but forming an angle. The air flowthen can pass through the gaps between the workpieces. The air flow thenpasses through the workpieces and travels down the robot handling unit.

The clean air delivery units can also deliver uniform clean air flowthrough the workpieces and system after being filtered. The storage areais designed to minimize or eliminate non-uniform, turbulent, or deadspace with little or no airflow with symmetric volumes, graduallychanges to the airflow direction, singularly airflow directions, andcontrolled venting. The exhaust venting rate can also be controlled toachieve a positive internal pressure for minimizing contaminationmigration into the storage area.

The air flow into the storage area can be divided into severalindependent partial air flows through, e.g. baffles in the vicinity ofthe storage locations. The air flow then can be directed so that eachair flow only encounter one workpiece to minimizing cross contamination.The arrangement of the air circulation system flowing clean air past theworkpieces prevents the accumulation of contaminants on the workpieceswhich can contaminate the workpieces.

FIGS. 9 and 10 show an exemplary arrangement of the containers 81 in thevertical direction. The handling unit 82 can achieve the differentvertical levels of the containers 81 by moving along two guide rails 88in vertical direction (perpendicular to the view level). The containers81 in this exemplary stocker include connections 90 for flowing cleaninggas. Connections 90 are arranged at the back of the containers 81, sothat the cleaning gas flushes the containers 81 from the back to thefront. In addition each connection 90 can include valve 91 forselectively opened or closed. It is thus possible to flush thecontainers individually with cleaning gas.

FIG. 9 shows an exemplary stocker 100 having the containers 81 arrangedone above the other and in a circle around a handling unit 82. In FIG.9, the wafers 20 are stored in horizontal position in the containers102. With horizontal storage of the wafers, the handling unit 82 doesnot have to turn the wafers 20 when taking in and out of the containers.The robot handling unit 82 is shown in two vertical positions, a topposition numbered 82 and a bottom position numbered 82′.

FIG. 9 also shows a blower and a filter unit 104 to provide a cleaninggas, preferably filtered clean air, to the interior of the housing 12.The blower and filter unit 104 receive ambient air, which is cleaned anddried and then flown afterwards into the interior of the housing. InFIG. 10, the cleaned air is flown over connections 90 at the back of theindividual containers 102. The air flow and the cleaning gas thus flowfrom the back of the container 102, out to the opened front and thendownward 106. As discussed above, this flow provides a nozzle effect forthe vertical storage, thus strengthens the cleaning efficiency. A goodflow can also be achieved with the horizontal storage, as presented inthese figures. Alternatively, the flow can be from the inside outward.

The stocker is a stationary stocker, provided with a robot handler,movable in the vertical direction (upward and downward) and in therotational direction. The stocker is provided with a plural number ofshelves for storing articles and positioned inward, for transferringarticles between a loadlock station and the stationary stocker.

FIGS. 11 and 13 show a top view of two exemplary stocker according tothe present invention. The stocker shown in FIG. 11 has the workpiecesarranged parallel, thus the inner gap of the workpiece compartment issmaller than the outer gap. The stocker shown in FIG. 13 has theworkpieces arranged radially, thus the compartments are parallel, withthe workpieces positioned closer at the inner circumference than at theouter circumference. FIG. 11 shows a circular arranged workpieces withtwo robot handling arms while FIG. 13 shows robot with only one handlingarm. The workpiece compartments are separate at the corners where systemcomponents can be located. The stockers as shown in FIGS. 11 and 13 hasclean air flow inward, from the storage wall, passing the workpieces,then to the robot handling unit, and downward to the exhaust.

A series of blowers can circulate clean air horizontally through therack, through the slots of the racks, and over the workpieces. Theblowers can be positioned in the upper or lower areas, and then air isdrawn downwardly or upwardly into an enclosure before travelinghorizontally into the workpieces. The air flow then exits verticallydownward adjacent to the racks. Some of the air can exit near the bottomof storage area through closeable louvres and some of the air can berecirculated back.

The horizontal flow through the workpieces prevents particles fromcoming to rest on the workpieces and the workpiece rack, and thevertically downward air flow removes particles from the stocker storagearea. The horizontal air flow is preferably flowing inward, from theoutside to the center of the stocker storage area. The outside isnormally the enclosure walls, thus is without any particle generation.The robot handling system is located in the center of the stocker, thusis positioned downstream of the air flow from the workpieces, andpreventing particles from damaging the workpieces.

The center area of the robot handling unit can have an air delivery uniton top, and an exhaust unit in the bottom to generate a downward pathfor the air flow. After exiting the workpieces, the air flow merges withthis downward flow and exhausts through the exhaust unit.

FIGS. 12 and 14 show a side view of two exemplary stocker according tothe present invention. The stocker in FIG. 12 has the workpiecespositioned horizontally while the stocker in FIG. 14 has the workpiecespositioned vertically. The robot unit is located in the middle of theworkpiece compartments with a downward air flow direction, downstream ofthe workpieces to avoid backflow and redeposit of particles. The airflow also flows through the workpieces from the outer wall.

The clean air is filtered with the filter elements closer to theworkpieces with “point of use” filters. The clean air delivery systemtypically includes fans (or blowers) and filter elements, or fan andfilter units (FFU). The units can have adjustments or controls for boththe pressure and the velocity of the generated air. The stocker includesa fan and filter unit at a top or bottom of the stocker system forfiltering, circulating and re-circulating clean air through the stockerstorage area to maintain the system in a clean room environment. In anexemplary, clean air from the fan filter unit is flowing down throughthe outer circumference of the storage area, then entering the slotsbetween the stored workpieces to carry away any particles from theworkpieces. The clean air passes by the front and back surfaces of thevertically or horizontal workpieces supported within the slots in thecompartment to clean the surfaces of the workpieces. The air is thenflowing down the center of the storage area.

The fan and filter unit can also provide an elevated pressure within thestocker storage area relative to the surrounding environment to ensureair flow from the stocker storage area to the robot handling assemblyand then out to the surrounding environment. Thus, any particulateswithin the robot, for example generated upon robot movement ormaintenance, will not enter into the stocker storage area.

With this flow configuration, the air flow only passes by the workpiecesonce. Thus any particles picked up by the air flow through a workpiecedoes not pass through another workpiece to prevent redeposition. Theclean air from the fan and filter unit only passes through a singleworkpiece and then exits through a bottom of the center robot handlingassembly. Moreover, with the robot handling in the center area, theparticulates are most likely generated where the contacts are, such aswhere the robot arm contacts the workpieces, or where the workpiecescontact the slots. The air flow system through the surfaces of theworkpieces flows the generated particles away from, and not towards, theworkpieces in the storage area.

In an alternative embodiment, a plurality of fan and filter units can beprovided within the stocker so that some units deliver clean airdirectly to the top storage areas, some to the middle storage areas, andsome to the bottom storage areas. The separation of fan and filter unitsminimizing possible cross contamination between the workpieces. Thestocker can include baffles for directing air flow in any desireddirections through the stocker storage areas.

During maintenance mode, when the enclosure is open for emergencyaccess, the air circulation system provides flow outward to the door toprevent outside air from entering the stocker storage area. The airflow's capacity is preferably high for providing positive air pressurewithin the storage area with the emergency door open. The door openingarea is also preferably small to enable the positive pressure, and tominimize back flow. Thus when the stocker door opens, the air flow ispreferably reverse so that air flow is now flow outward, preventingoutside air from entering the storage area. Center exhaust can be closedto ensure that the air flow direction is outward from the workpiecesstorage area.

Further, the storage area can be partitioned into a plurality ofsections based on cleanliness, for example, a top section for ultraclean storage, a middle section for normal clean storage, and a bottomsection for dirty storage. The flow configuration can be designed forminimizing cross contamination between these sections. The separationcan be accomplished with baffles, with holed partition walls, or withair curtain configuration. The ultra clean section can be located in thebottom near the exhaust since with a high exhaust rate, there is lessparticulate generation.

Static reduction assembly such as ionization system can be added withinthe air flow for reducing the build up of static electricity to preventcharge particle attraction, and electrical static discharge. The stockercan include alarms for sensing the condition of the stocker storagearea. For example, air flow sensors can sense the absence of reduced airflow to activate an alarm. Particle sensor might also activate an alarmif sensing exceeding particle limits.

The present invention discloses an article transfer and storage system,comprising a stationary stocker capable of storing a plural number ofarticles, surrounding a robot assembly located on the inner side of thestationary stocker.

The stock unit according to a second embodiment of the invention has aplurality of stockers and also a transfer means for transferringcarriers to and from the shelves incorporated in these stockers.

What is claimed is:
 1. A stocker for storing a plurality of flatsubstrates, each flat substrate comprising two opposite flat surfacesand a peripheral edge, the stocker comprising: a storage compartment forholding the flat substrates in a vertical direction; an edge gripsubstrate handler for transferring the substrates, the edge gripsubstrate handler handling a substrate by the peripheral edge withoutextending to the flat surfaces; an end effector substrate handler fortransferring the substrates, the end effector substrate handler handlinga substrate by extending to a flat surface of the substrate; a load portfor providing substrates to the storage compartment, wherein the loadport is configured for holding the substrates in a horizontal direction,wherein the load port is configured so that the substrates areaccessible by the end effector substrate handler and are not accessibleby the edge grip substrate handler; a station for receiving a substrate,wherein a substrate in the station can be handled by the edge griphandler and the end effector handler, wherein the edge grip substratehandler is designed to access substrates in the storage compartment andin the station, and wherein the end effector substrate handler isdesigned to access substrates in the load port and the station.
 2. Astocker as in claim 1 wherein the station comprises a substrate support,wherein the substrate support is configured so that a substrate disposedon the substrate support is accessible by the edge grip substratehandler and by the end effector substrate handler.
 3. A stocker as inclaim 1 wherein the edge grip substrate handler comprises a claw-liketip to hold the substrate by the peripheral edge.
 4. A stocker as inclaim 3 wherein the claw-like tip is configured to handle substrates inthe storage compartment having a substrate spacing equal or less than 5mm.
 5. A stocker as in claim 1 wherein the edge grip substrate handleris configured for handling the substrates in the compartment having asubstrate spacing equal or less than 2.5 mm.
 6. A stocker as in claim 1wherein the storage compartment comprises a recess which is configuredto accept a retainer for holding the substrates in place duringmovements of the storage compartment.
 7. A stocker as in claim 1 whereinthe station comprises a pre-aligner.